Nikon D200 or Canon 5D?

Karl is spot on - my own experience exactly. All zooms are a compromise underwater and can only be optimised at one focal length behind a dome port. Whilst they can produce very acceptable results, they do need to be used with a degree of caution and are at their best when corner content is minimal or unimportant.

I'm spending too much time adusting and resizing files today, to say nothing about wrirting DVDs. Must get out from behind my computers!

i made the decision for Canon before digital and have not regretted it

even though Nikon is doing a remarkably good job playing catch-up to Canon, they just don't have the capitalization and R&D to match Canon's ability to develop and manufacture their own sensors and processors - Canon will continue to stay ahead and may move even farther ahead in resolution, noise, dynamic range, and color

the only reason to buy Nikon is if you have a lot of Nikon glass